Fix the error-pattern in compile-fail/bad-main.rs. Un-XFAIL

This is also tested by compile-fail/main-wrong-type.rs but the type signatures
are slightly different, so I guess it's worth holding on to.

src/test/compile-fail/bad-main.rs

@@ -1,6 +1,3 @@
-// xfail-stage1
-// xfail-stage2
-// xfail-stage3
-// error-pattern: bad type signature
+// error-pattern:Wrong type in main function
 
 fn main(x: int) { }